What did I do wrong?
 

Recently I screwed up and hit the fence at a HPDE event at Sandown in Melbourne. Is anyone out there able to take a look at this data and tell me what I did wrong? I don't have video but I do have data from my Aim DL Solo.

Stock car + MCA Red coil overs and semi-slick tyres.

It was only the first session and I was taking it easy. From what I can tell I:

- lifted off early coming towards turn 6. I recall thinking 'its first session so back off early'.

- touched the brake to wipe off speed. I looks like I was off the brake before the corner entry.

- then??? It all happen so fast I don't have a good understanding of what went wrong.

I'm heading back to Sandown in a few weeks. I sure as hell don't want to screw this up again.

Adrian

What was the ambient temp?

-mike

Based on the table on the left of the first image, IAT was 19 C. Ambient should be close to that, maybe slightly below.

This is where video really helps. It could be lots of things - an oil slick you didn't see, cold tires, VSC or e-diff weirdness, or a bad input you made that you don't remember. Even after almost ten years of performance driving, I'm still amazed at some of the things video/photos will catch me doing in the car that I don't realize.

Touching the brakes at the wrong time can certainly upset the car. It's tough to see with the scaling of the longitudinal accel graph but I think you're still slowing down considerably when you turned in. With the front loaded up and the rear unloaded I bet you entered into a slide that you didn't really notice until too late, you may have thought you were just rotating the car well.

You should rarely, if ever, just coast - once you're off the brakes it's good practice to start feeding in throttle, even if it's only 5-10%. That will help transfer some weight back to the rear, and remember: the fastest lap is the one you use the go pedal the most!

Where did you go off? Turn 6 or turn 7?

Judging from your description, and from what I can tell reading the data, it looks like the brake application might have been just barely enough to upset the car's balance, causing a slight rotation that you countered a little late, then it went haywire. The tire's slide might have been subtle enough that you didn't really feel it at first.

You can see where you hit the brake, there's a slight amount of lateral accel right before you release the pedal at 0:54 where a (assumed RH) slide begins, then more lateral accel with minimal steer input through 0:56, this is where the slide builds steam and becomes difficult to overcome. About halfway through the RH slide at 0:56 you begin to countersteer and slightly over correct (or the car's inertia whips back) and you snap back to slide LH at 0:58. 0:58 is where it appears you went offroad, and 0:59 started panic braking even though it didn't do anything. Slide for 2 more seconds, then hit the wall at 1:01.

Video would be definitive, but this is the best I can tell from your limited description and the data...

Good eye, you pieced together a couple things I didn't spot. One thing I see now is that steering input after the initial catch of the slide doesn't go the other way until lateral acceleration has already started swinging the other way. That's a classic overcorrection - once you start arresting the slide, you need to back out of that steering input before the car is straight or you're going to whip the car around.

Do you have other data for a normal lap? The braking application @ 53.5 has the same ramp angle as your panic braking moment @ 59.5 albeit not as hard.

Without video or other data for comparison, the ramp angle suggests you "stabbed" the brake pedal instead of "rolling onto the brakes" and that may have upset the car which can easily happen if one caliper grips slightly differently than the other under initial load. When you stab the breaks that difference between the two sides gets exaggerated and can move the rear of the car. Also the compliance in bushings can cause wiggle under breaking as well or the camber of the pavement.

You are doing over 100mph at that moment and there's a lot of wind under the car as well.

This is all guessing but I've had my tail step out lots of times under braking for a variety of reasons. The face that your lateral load data changes at the peak of your initial braking application and then snowballs from there suggests that it was the braking application (technique, function of the pads, compliance of bushings) that induced this.